At above 1950 intraocular lenses were introduced. Such lenses are man-made, each comprising a plastic lens blank having retention devices attached thereto. They are utilized to replace the natural lenses of patients suffering from cataracts. Thus, in the use of such lenses the diseased natural lens is removed, and, at the same time an intraocular lens is surgically inserted to replace the natural lens. Intraocular lenses are advantageous in that they are optically ideal, because the placement of the artificial lens where the natural lens came from restores the patient to almost normal vision as distinguished from prior cataract operations which simply removed the lens and depended upon heavy cataract glasses or contact lenses to restore vision. The cataract glasses were subject to causing over magnification and distortion such as tunnel vision. Contact lenses are unsuitable for many patients and at best cause some magnification discomforts. For these reasons use of intraocular lenses is of increasing importance in the field of opthalmological surgery. Because of the advantages mentioned herein intraocular lens are coming into more general use and are now a preferred form of surgical treatment for cataracts.
Intraocular lenses are each comprised of a disc of appropriate material, such as a low monomer clear acrylic plastic. One specific example of a medically approved material is polymethylmethacrylate, which is a thermoplastic acrylic suitable for implantation. The plastic disc is carefully machined to an appropriate diameter to fit the lens cavity of the eye and to provide a flat circular base and a convex front face of thickness and curvature to give a lens of desired diopter rating. Such lenses are provided with two or more loops for retention in the eye of the patient and may also be provided with metal locking pins to assist in retention. The loops may be made of thin wires or lines of appropriate metal or plastic material. Typically, metal loops are made of platinum iridium wire and plastic loops are made of thermoplastic material (an approved material is sold under the trade name SUPRAMID).
Although specific dimensions are not critical to understanding or practice of this invention it should be understood that lenses of the type under discussions are quite small, light and delicate. Intraocular lenses are provided with a variety of retention arrangements to provide for patients having different problems. One common type is called the extracapsular lens and is surgically positioned in the patient's eye utilizing capsular fixation. Extracapsular lenses normally have one pair of opposed outwardly disposed loops, generally of metal wire such as platinum iridium and which are designated posterior loops because the ends are attached into and through the rear face or base of the lengs. The four ends of the two loops are generally arranged in a square pattern at distances of about 1 mm. from the center line of the lens, outside the line of vision of the wearer. The loop wires are of 0.15 to 0.20 mm. diameter and extend axially downwardly from the base about 0.6 mm. and are then curved outwardly and downwardly on about a 30 mm. radius curve to about 0.15 mm. from their ends. The length of the overall assembly measured to the ends of the two-loops is 7.5 to 8 mm. A variation is the intracapsular lens which is a four loop lens which is surgically attached by "iris-on-iris" fixation and a loop suture in the iridectomy. The intracapsular lens has all of the structure previously described but is provided with an extra pair of loops, designated anterior loops. These are generally made of plastic line extending from the sides of the lens disc and are positioned concentrically outwardly relative to the posterior loops.
State of the art intraocular lenses are characterized in that all of the loops are attached by press or slip fitting the wires into holes drilled through the lens. In the state of the art lenses, attachment of posterior loops is generally by insertion of the ends of the loops into holes drilled entirely through the lenses from the base toward the face of the lens. Such holes are drilled entirely through the lens from the back surface of the lens through the curved lens face and are beveled or deburred at the ends, the bevelling typically causing material displacement or distortion of an area 3 times the diameter of the iris. Typically, the material of such loops is of a diameter equal to or slightly larger than the diameter of the through-bores and are press or slip fitted into the holes, causing displacement of material in some cases. Two such loops are usually used, providing four ends which are attached, as previously described, generally in a square pattern.
Prior art anterior loops are typically of resilient thermoplastic material, one approved material for this purpose being sold under the trade name "SUPRAMID". A length of line of such material is inserted through two holes drilled through the sides of the lens disc as opposed or parallel chords in the circular periphery of the side walls thereof. Typically two such loops are formed of a single length of line which passes entirely through one of said holes and the ends of which are slip fitted into a butting relationship within the other hole.
Aside from the two specific lens and loop configurations described above, many other configurations have evolved, depending upon either the preferences of surgeons using such lenses or upon particular patient requirements. Thus, as will be better described hereinafter, lenses may have one to four or more loops. Moreover, some lenses are provided with wire extensions having enlarged balls at the ends thereof, called locking pins, such pins being fitted into the side or anterior surfaces of lenses and serving to mechanically lock tissue to loops or to be mechanically embedded in tissue. However, in the prior art, all such attachments, whether loops or pins, were attached by press fitting the wire or other material into pre-bored holes. Prior to the present invention the described press fitting techniques were the only mode available for effecting the connections in intraocular lenses, since glues cannot be used for medical and optical reasons such as the dangers of discoloration, contamination, toxicity and the like.
One disadvantage of all previously described prior art intraocular lenses is instability, i.e. the possibility of press fitted loops and/or pins pulling out in handling during surgery or afterwards. Moreover, the press fits of some loops and/or pins may cause displacement of plastic material, causing distortion, stress risers and possible eventual striations in the lens, which would impair the vision of the wearer. This latter disadvantage is accentuated in the posterior loop structure wherein the ends of metal wires are forced through chamfered through bores of equal or lesser diameter. This reqiured mode of assembly causes frizzing of the wire ends and burring of the hole just below the face of the lens. Moreover, the chamfers used to assist assembly and for smoothing causes stress risers which may lead to progressive striation of the lens with increasing impairment of vision. The parent invention relates specifically to improved methods and apparatus for connecting retention loops and locking pins to intraocular lenses of the type described. Reference is made to applicant's prior U.S. patent application, Ser. No. 599,112, filed July 25, 1975, which issued Nov. 30, 1976, as U.S. Pat. No. 3,994,027, disclosing and claiming as articles of manufacture intraocular lenses of types which can be manufactured by the methods and apparatus of the present invention. However, the invention is not intended to be limited as to any specific pin and/or loop arrangement since the gist of the invention is in the apparatus for and methods of effecting the connections of such pins and/or loops to the lenses, whatever the configuration.